20 



BKITISH FOSSILS. 



Thus, leaving open the question as to the identity of Ccelacanthus 

 with Undina, and also that whether Uronemus and Hoplopygus 

 (which I have not seen, and concerning which no details are given 

 by Agassiz) are Coelacanths, or not ; it appears to be certain that 

 fishes closely allied to Coelaeanthus granulatus, and known under 

 the generic appellations of Undina and Macropoma, form an exceed- 

 ingly well-defined family, to which the term Cgelacanthini may 

 with propriety be restricted, and which has ranged in time, with 

 remarkably little change, from at least as early as the Permian 

 formation to the Chalk, inclusive. 



The Coelacanthini, as thus understood, are no less distinctly sepa- 

 rated from other fishes than they are closely united to one another. 

 In the form and arrangement of their fins; the structure of th^ 

 tail and that of the cranium ; the form and number of the jugular 

 plates ; the dentition ; the dorsal interspinous bones ; the pelvic 

 bones ; the ossified air bladder ; t^e Coelacanthini differ widely from 

 either the Saurodipterini, the Glyptodipterini, or the Ctenododipte- 

 rini ; but, on the other hand, they agree with these families and 

 differ from almost all other fishes, in the same respects as those in 

 which the several families just mentioned, have been shown to agree 

 with one another ; viz., the number of the dorsal fins, the lobation 

 of the paired fins, the absence of branchiostegal rays, and their 

 replacement by jugular bones. 



Their special affinities among these three families appear to me 

 to lie chiefly with the Ctenododipterini : the scales, the arrangement 

 of the teeth, and the form of the lower jaw in the two families pre- 

 senting many curious analogies. 



The Glyptodipterine family contains, as we have seen, both 

 eycliferous and rhombiferous genera. Following out the alliances of 

 the former subfamily, we have found reason to include the eyclife- 

 rous Ctenododipterini and the eycliferous Coslacanthini in the same 

 larger, or subordinal, group with the Glyptodipterini. If, on the 

 other hand, we now trace out the congeners of the rhombiferous 

 subfamilies, we arrive, as has been seen, at the Saurodipterini ; 

 and the question now remains, what other rhombiferous Ganoids 

 naturally arrange themselves at this end of the series ? 



So far as I am aware, there is no other fossil rhombiferous Ganoid 

 which comes within the scope of the sum of characters common to 

 the Saurodipterini, Glyptodipterini, Ctenododipterini, and Coelacan- 

 thini ; but among recent fislies there is one, Polypterus, which very 

 nearly approaches the required standard, and is unquestionably 

 closely allied to the Saurodipterini. 



